Markov chain Monte Carlo Detector Tomography applied to a NbTiN nanobridge

Abstract

We demonstrate the use of a flexible and highly accurate Markov chain Monte Carlo Quantum Detector Tomography method as a minimization algorithm to best describe the response of an efficient $120nm$ wide NbTiN superconducting nanobridge single photon detector. Separation of the internal quantum efficiency and external quantum efficiency is possible due to the difference in saturation behavior of an ideal 1-photon threshold detector as compared to a detector with non-unity 1-photon internal quantum efficiency. From a statistical analysis of our measurements (at $T=4.23\pm 0.01K$, $I=29.4\pm 0.1\mu A$, $I/I_{\text{switch}}=0.90\pm 0.01$) we find an external quantum efficiency $\eta =(1.60\pm 0.05)\cdot 10^{-6}$, a 1-photon internal quantum efficiency $p_1=0.568\pm 0.008$ and unity multi-photon (2 or more) internal quantum efficiency.

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